Synthesis of Zinc Hydrazonide Complexes

The zinc hydrazonide complexes [ClZn(CH2C(Me)NNMe2)(py)]2, [ClZn(CH2C(t-Bu)NNMe2)]2, [Zn(CH2C(Me)NNMe2)2]2, Zn(CH2C(i-Pr)NNMe2)2, and Zn(CH2C(t-Bu)NNMe2)2 were synthesized by salt metathesis reactions, and the coordination polymer [EtZn(CH2C(Me)NNMe2)]n was obtained from the reaction between excess ZnEt2 and [Zn(CH2C(Me)NNMe2)2]2. Single crystal X-ray crystallography studies revealed that the hydrazonide ligands were bound to zinc as chelating alkyl ligands. The ligand precursor [Li(CH2C(i-Pr)NNMe2)(THF)]n was also structurally characterized. In the anion of [Li(CH2C(i-Pr)NNMe2)(THF)]n, the hydrazonide ligand in [EtZn(CH2C(Me)NNMe2)]n, and the bridging hydrazonide ligands in [Zn(CH2C(Me)NNMe2)2]2 and [ClZn(CH2C(Me)NNMe2)(py)]2, there is evidence for three-center charge delocalization. In solution, the dimer [Zn(CH2C(Me)NNMe2)2]2 is in equilibrium with the monomer Zn(CH2C(Me)NNMe2)2. The thermodynamic parameters ΔH° = 55.8(2.9) kJ/mol, ΔS° = 144(2) J/mol K, and ΔG°298K = 13(2) kJ/mol for the equilibrium were obtained from a variable temperature 1H NMR study.